Vascular disease is the leading cause of death in the United States. Neural-tube defects are a major contributor to perinatal morbidity and mortality. Elevated levels of plasma homocysteine (a non-protein amino acid) have been found to correlate with an increased risk of NTDs and vascular disease. Methionine synthase (MS) catalyzes the vitamin B12 dependent, interconversion of homocysteine and 5-methyltetrahydrofolate to methionine and tetrahydrofolate. This is one of the few homocysteine consuming reactions in the body and reduced MS activity is predicted to lead to increased plasma homocysteine. We have cloned the human MS gene and demonstrated that hyperhomocysteinemia in a subset of patients is in fact due to mutations in the MS gene. Families with children affected with NTDs have been screened to determine if MS plays a role in NTD. We did notfind a connection between variants in MS and NTDs. We are now testing to see if the enzyme that acts with MS, MS-reductase plays a role in NTD. We also plan to asses avariety of candidate genes for a role in NTDs in a large collection of Irish NTD families (> 200 cases plus their unaffected parents). Rather than screening each gene for mutations, which is labor intensive and requires knowledge of the genomic structure of each gene, we are makers linked to the genes to test for association and/or transmission disequilibrium. Genes presently under study include methionine synthase (MS), methionine synthase reductase (MTRR), cystathionine-B-synthase (CBS), S-adenosyl- L-homocysteine hydrolase (SAHH), transcobalamin II (TCII), and methionine adenosyltransferase (MATa1). We will follow up any positive associations revealed by the polymorphic marker studies by screening the corresponding linked candidate genes with conventional mutation detection methods. In addition to the human genetic studies, we have used homologous recombination techniques to create a mouse model of MS deficiency. The phenotype of this mouse is currently being investigated. - spina bifida, infant mortality, pediatric research, genetics, heart disease - Human Subjects